1. Field of the Invention
The present invention relates generally to improvements in anti-gas locking devices for downhole pumps and, more particularly, but not by way of limitation, for downhole pumps used to raise mixtures of oil and water to the surface from an oil well.
2. Brief Description of the Prior Art
The fluids in the borehole of an oil well generally consist of a mixture of oil and water in which gases are guite often dissolved. These dissolved gases can be evolved by mechanical working of the liquid components of the fluid; for example, as will occur when the fluids are pumped to the surface, and such evolution of dissolved gases generally creates a problem where the pump used to raise well fluids is of the downhole centrifical type. The operation of this type of pump depends upon the pump being filled with a liquid so that, if evolved gases displace the liquid in the pump, the pump will be incapable of delivering fluids to the surface and, equally important, of clearing the gases so that a liquid can enter the pump. The result is that the pump is driven to no effect and is said to be gas locked.
In order to prevent the occurrence of gas locking in a downhole pump, it is known to equip the pump with an anti-gas locking apparatus that separates gas from the well fluids before such fluids enter the inlet of the pump and examples of such apparatus have been disclosed in U.S. Pat. No. 3,175,501 and U.S. Pat. No. 3,291,057, both of which are to Joseph T. Carle. An anti-gas locking apparatus of the type disclosed by Carle generally comprises a tubular sleeve through which a drive shaft for the pump passes from a downhole motor which is attached to the bottom of the anti-gas locking apparatus. The sleeve is disposed below the pump inlet and is mated therewith to discharge fluids introduced into the sleeve into the pump inlet. In addition, the anti-gas locking apparatus includes a housing which extends concentrically about the sleeve, and has openings into the well near its upper end so that well fluids can enter the housing, and a cross-over assembly that communicates the sleeve and housing at the lower end of the sleeve. Well fluids enter the openings in the housing, travel downwardly to the cross-over assembly, and reverse direction while passing therethrough to enter the lower end of the sleeve. The direction reversal tends to cause dissolved gases to be evolved from the well fluids in portions of the cross-over assembly underlying the annulus between the sleeve and housing so that such gases can escape through the housing openings to the well.
While most of the evolution of gases from the fluid takes place at a position in the anti-gas locking apparatus which will permit escape of the gases to the well, some gas will remain with the oil-water mixture and can be evolved at locations that will cause the gas to enter the sleeve. This residual gas can build up in the pump to cause gas locking of the pump and the prior art anti-gas locking devices are generally constructed to include some means for removing residual gases as they are evolved. The inclusion of such means, while effective for preventing gas locking, can, however, lower the efficiency of the pump or increase the cost of manufacturing thereof. For example, where a means is provided near the inlet of the pump to return the evolved residual gases to the well, such means will also generally return a portion of the pumped liquids to the well so that energy expended in pumping these liquids will be wasted.